1. Field of the Invention
This invention relates to a cross groove type constant velocity joint whose grooves of an outer race cross grooves of an inner race in a circumferential direction.
2. Discussion of the Background
A cross groove type constant velocity joint comprises an outer race with plural outer grooves on its inner surface, an inner race with plural inner grooves on its outer surface, plural balls between the outer and inner grooves and a cage with plural windows to hold the balls between the outer and inner races. The outer grooves of the outer race are twisted about the rotational axis of the outer race and the inner grooves of the inner race are oppositely twisted about the rotational axis of the inner race. The outer race is formed to a cuplike shape by forging, and then the outer grooves are roughly machined by a cutting tool and are ground by a grinding tool. The grinding tool is a sphericity whose diameter is a little larger than the diameter of the balls, because the balls roll on the grooves. Thus, to prevent the grinding tool from interfering with the innermost end of the cuplike outer race, concave recesses are continuously formed at the back of the respective outer grooves before grinding the outer grooves. The respective recesses are generally a partial sphericity whose diameter is larger than the diameter of the grinding tool. That is, the recesses have enough room for the balls to drop into. Thus the constant velocity joint has a restriction to prevent the balls from dropping into the recesses when a joint angle of the constant velocity joint reaches a predetermined angle. The predetermined angle of the joint angle may occur, for example, when an operator lifts the constant velocity joint in order to assemble it into a vehicle. If the constant velocity joint does not have the restriction, the outer race may be held by a shaft connected with the inner race so that some of the balls may drop into the recesses. In such an event, the operator must dismantle and reassemble the joint.
Japanese utility model application publication No. H01-69916, for example, discloses a boot having a metal part or a stiff boot in order to restrict the joint angle. And Japanese utility model application publication No. H06-32755 discloses a circlip for the restriction of the joint angle. These prior arts need an additional element such as the circlip or the special boot with metal/stiffness, which increases the cost and complexity of the assembly process.